ITC == Introduction To Cryptography

Pseudorandom ...

ITC == Introduction To Cryptography

Pseudorandom Number Generation And Stream Cipher

Algorithm Design

  • Purpose-built algorithms
    • 專門用來產生 pseudorandom number (bit stream)
    • 最具代表性: RC4
  • Algorithms based on existing cryptographic algorithms
    • Symmetric block ciphers
    • Asymmetric ciphers
    • Hash functions and message authentication codes

Pseudorandom Number Generators

  • Linear Congruential Generators
X_{n+1} = \left (aX_{n}+c \right ) \mod m  
  • Blum Blum Shub Generator (BBS Generator)

Pseudorandom Number Generation Using A Block Cipher

  • PRNG Using Block Cipher Modes of Operation
    • CTR Mode
      CTR Mode
    • OFB Mode
      OFB Mode

Stream Ciphers

  • A key is input to a pseudorandom bit generator that produces a stream of 8-bit numbers that are apparently random.

  • The output, called keystream, is combined one byte at a time with a plaintext stream using the bitwise XOR operation.


RC4

  • A stream cipher designed in 1987 by Ron Rivest for RSA security.

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